[TOKYO] Japanese Prime Minister Yoshihide Suga's ruling party will hold a leadership election on Sept 29, party officials said on Thursday, ahead of an expected challenge from former foreign minister Fumio Kishida.

Mr Suga, 72, took office last September with support of about 70 per cent but his ratings have sunk below 30 per cent as Japan battles its worst wave of Covid-19 infections and many of his Liberal Democratic Party (LDP) lawmakers fear for their seats.

Mr Suga has said he plans to seek re-election as LDP president.

Victory would ensure he remains premier because of the LDP's majority in Parliament's lower house.

LDP Secretary-General Toshihiro Nikai, who was key to Mr Suga's victory last year, said on Wednesday he still backs the prime minister. Other party bosses, including former premier Shinzo Abe and Finance Minister Taro Aso, have not commented publicly.

Mr Kishida, a soft-spoken lawmaker from Hiroshima, had been seen as the preferred heir to Mr Abe, who stepped down last year as prime minister citing ill health. But Mr Kishida lost the ensuing party poll after factions coalesced around Mr Suga, who had been Mr Abe's right-hand man for eight years.

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Mr Kishida typically ranks low in surveys of voters' preferred next prime minister, well below other possible rivals such as Administrative Reform Minister Taro Kono, who is leading Japan's vaccination rollout, and former defence minister Shigeru Ishiba.

"Unless they chose someone like Ishiba who is more popular with the public, it will be hard to recover lost support," said Hiroyoshi Sunakawa, a professor at Tokyo's Rikkyo University.

Unlike last year, this time grass-roots LDP members will vote along with the party's members of Parliament.

Long-shot contenders to replace Mr Suga include former internal affairs minister Sanae Takaichi, an Abe disciple aiming to become Japan's first female premier, and conservative former education minister Hakubun Shimomura.

Mr Suga's dream scenario had been to call a general election in September after hosting the Olympics but that was upended by the Covid-19 surge. The Sankei newspaper said on Thursday that election, which must be held by Nov 28, would be held in October or later.

Hiroyuki Ueno, senior strategist at Sumitomo Mitsui Trust Asset Management, said multiple candidates could make the LDP race more interesting but might not change the outcome.

"My sense is, most people in markets expect Suga to win unless he decides to quit by himself," Mr Ueno said.

The LDP-led coalition is unlikely to lose its majority in the powerful lower house, but forecasts suggest that Mr Suga's party could lose the majority that it holds on its own, an outcome that would weaken whoever is leading the LDP.

REUTERS